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262

Slide Valves and Flywheel.

to proper* depth. Reverse the work, as at B, and set truly with
the turned face. Turn the inner surface and the smaller diameter.
Now set the cover, end up, on the marking table, as at c, until
the boss is horizontal. Having spanned the hole and found its
centre, scribe the centre line along the boss and on to the cover.
Scribe also the seating for the slide bars and the centres of the
gland studs. Now turn the cover through 90°, by measuring from
a square, as at D, and scribe the centre line across. Mark also
the slide bar seatings, and divide out the stud holes; then drill
the bolts and studs, and slot the slide bar seatings. Lastly, scribe
through the stud holes on to the cylinder flanges. The back cover
is turned, as at E and F, and similarly marked, and the gland
tooled as previously described at Fig. 238.

XXXI.    Main Slide Valve (Fig. 266).—Lay horizontal,
as at B, scribe centre of boss and thickness of valve, and plane
both sides.    Set up, as at c, till the bosses are level, and scribe
the centre all round ;  line also the top and bottom surfaces.
Turn to the position D till the boss is quire vertical, and scribe
the centre line round    From this, line the height of boss at top
and bottom..   Re-scribe the hole for the spindle at both ends,
which is much larger than the valve spindle, to allow for wear of
valve.    Next set up on an angle plate in the drilling machine,
as at E, till vertical, and drill the hole right through, knifing at
the same time.    Plane the top and bottom surfaces.    Line out
the ports by means of a template, and finish their edges by
hand.

XXXII.    Expansion Slide Valve (Fig, 267).—Set level,
as at B, and scribe the boss centres and the face.    Square up the
edge, measuring from the centre, and join this along the top.
Next set vertically, as at c, scribe the centre, and line thickness
of boss seatings.    Drill, knife, and plane as before, finishing the
edges to template.

XXXIII.    Flywheel (Fig, 268) requires very little descrip-
tion.    It is simply bolted centrally by the arms to a large face
plate, as shewn at A, the boss bored, and both boss and rirn faced.
It is next reversed, the other side faced, and the rim turned, as
in previous similar pases, the curved surface' being given by a
careful hand feed.    (For keyway cutting, see Appendix L>$* 754.)